2.1.382 Part 1 Section 17.14.35, uniqueTag (Unique Value for Record)

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a.   The standard does not define the contents of this element.

Word defines this element to contain a val attribute that is defined by the XML Schema base64Binary datatype.

b.   The standard says that this element is used to maintain a relationship between the records within an external data source and a given merged WordprocessingML document.

Word uses this element to maintain a relationship between the records within an external data source and a given source WordprocessingML document.

c.   The standard does not state how this element should be populated when the column containing unique data for a record is empty.

Word computes the unique tag, when empty, to be a base64-encoded value using the following algorithm:

Utility function 1:

 #define nPrimeLast 4294967291
 __int32 LHashMM( __int32 l, __int32 dl )
 {
         l = 131 * l + dl;
  
         if (l >= nPrimeLast) {
                 l -= nPrimeLast;
         }
  
         return l;
 }

Utility function 2:

 __int32 LGetHashWz(const WCHAR *wzText)
 {
         int cch = lstrlen(wzText);
         __int32 lhash = 0L;
  
         for (int i = 0; i < cch; i++) {
                 lhash = LHashMM(lhash, wzText[i]);
         }
  
         return lhash;
 }

Utility function 3:

 __int32 DwRowHash(thisRow) 
 {
         __int32 lwHash = 0L;
         for(int i = 0; i < TotalNumberOfColumnsInTheDataSource; i++) {
                 Retrieve the value in the i-th column of thisRow as a Unicode String wzData;
                 __int32 l = LGetHashWz(wzData);
                 if(l) {
                         lwHash = LHashMM(lwHash, l);
                 }
         }
         return lwHash;        
 }

Unique tag computation algorithm:

WCHAR wzUniqueTag[64] = {0};

*((__int32*) wzUniqueTag) = DwRowHash(the_row_containing_this_record);

return the wzUniqueTag as the uniqueTag;